Research On Integrated Design Of Aerodynamic And Stealthy Performance With Intake And Exhaust For Flying-Wing Layout

The aerodynamic performance of intake-exhaust system has a direct impact on the operation of the engine,and its layout will also directly affect the overall aerodynamic performance of aircraft.Meanwhile,as an electrically large cavity,the intake-exhaust system is one of the main electromagnetic scattering sources of the aircraft in the forward and backward direction.The Radar Cross Section(RCS)created by intake-exhaust system takes a great proportion in the overall aircraft RCS,which will have a great impact on survivability.Therefore,designing a reasonable intake-exhaust system layout to acquire the good aerodynamic and stealthy performance is an emphasis in the research of the modern stealth aircraft.Based on the high aspect ratio flying wing Unmanned Aerial Vehicle(UAV)with twin-engine,series of research on integrated design of aerodynamic and stealthy performance with intake-exhaust for flying-wing layout is carried out.This dissertation carries out several aspects of research work as follows:(1)The numerical simulation method for aerodynamics based on the three-dimensional compressible Navier-Stokes(N-S)equations and several numerical simulation methods for electromagnetic scattering characteristics are presented.Firstly,based on the finite volume method,the aerodynamic numerical simulation method is built with Roe space discrete and implicit LU-SGS time stepping scheme,and it also adopts various boundary conditions.Secondly,several kinds of stealthy numerical simulation methods are discussed,and they are Multilevel Fast Multipole Method(MLFMM),Physical Optics(PO)and Shooting and Bouncing Ray(SBR)respectively.And we also study their mechanism,calculation precision and scope of application.Finally,experimental and numerical results are compared to verify the methods for aerodynamic and electromagnetic scattering calculation.(2)In order to solve the design problem of superb aerodynamic and stealthy performance,research on aerodynamic and stealthy characteristics and design for flying wing UAV is conducted.And then a kind of fuselage leading edge similar to eagle mouth is proposed for flying wing UAV,which obtains both good aerodynamic and stealthy performance,and it is used as the basis for later design of conformal intake-exhaust system.Focusing on the big bulge in the fuselage of the high aspect ratio flying wing,the design of flying wing layout is carried out based on stealth off-design and load arrangement respectively.As we know,the high aspect ratio flying wing UAV presents different electrically size features under different radar frequencies,and so the corresponding methods for RCS prediction are established,which are validated by stealth test of a scale flying wing model.(3)In order to acquire good aerodynamic performance and stealthy performance integrated into the intake-exhaust system,one idea of conformal integration design is presented,and it is applied to design the conformal intake-exhaust system for twin-engine flying wing UAV.Firstly,based on the conventional inlet design criteria,design method of S-shaped inlet is established combining the super-ellipse equation.Then it is adopted to design regular shape(rectangular intake to round exit)S-shaped inlet,and five inlets with different centerline and cross-sectional area are constructed,and it is preliminarily verified that the established inlet design method is effective.Secondly,based on the inlet design method,conformal inlets for the twin-engine flying wing UAV are designed.Finally,considering the compatibility of aerodynamic,electromagnetic stealth and infrared stealth,conformal asymmetric nozzles of large aspect ratio for flying wing UAV are also constructed.(4)In order to obtain better aerodynamic performance and higher propulsion efficiency,research on aerodynamic characteristics and design is carried out for conformal intake-exhaust system of twin-engine flying wing UAV.Firstly,based on the principle of aero-propulsive balance and isentropic flow assumption,numerical simulation method of power for the intake-exhaust system of UAV is developed by introducing pressure boundary condition to simulate the intake and exhaust effects of engine and adjusting the power parameters combining the principle of aero-propulsive balance.And then the pressure boundary condition is verified through comparing the calculation with experimental results of conformal inlet and expansion nozzle respectively.Secondly,based on the established simulation method of power,research on aerodynamic characteristics and design are carried out for conformal inlet and nozzle of twin-engine flying wing UAV.Then based on conformal circular-rectangle nozzle,we study a new thrust vector control mode,namely the conceptual design of the nozzle gas rudder.In order to further promote the internal flow characteristics of conformal intake-exhaust system,study on conformal asymmetric S-shaped inlet design and optimization is carried out.A new inlet parameter method is proposed by present a new variation of the centerline and cross-sectional area,and it adopts the Transfinite Interpolation(TFI)and constructs the optimization system by introducing updating the sample and making multi-round optimization.Finally,in order to further enhance the overall aerodynamic performance of flying wing UAV coupling the intake-exhaust system,research on multi-bump design and drag reduction optimization is carried out based on Free-Form Deformation(FFD)technology.(5)Research on electromagnetic scattering characteristics and design is carried out for conformal intake-exhaust system of twin-engine flying wing UAV,and an effective numerical method of electromagnetic scattering characteristics is constructed for cavities of different electrical size.Firstly,the numerical calculation method of electromagnetic scattering characteristics for the cavity is built,and it is verified by the stealth test combining with the oblique import inlet of 45°.Secondly,the S-shaped inlet with rectangular intake to round exit,which has the sanme size of the conformal inlet of UAV(the cross-sectional area of the intake and exit are the same)is constructed.And then research on the electromagnetic scattering characteristics influence of centerline and cross-sectional area is carried out based on MLFMM,and we also analyze the scattering mechanism.Finally,combining the full-size large aspect ratio flying wing UAV coupling conformal intake-exhaust system,research on electromagnetic scattering characteristics and design is carried out for inlets with different entrance shape and asymmetric nozzles with different area ratios.And the numerical simulation method is further verified by the stealth test of flying wing UAV coupling the rectangular inlet.(6)Due to the signficant enhancement of scattering in the forward region for the twin-engine flying wing UAV coupling conformal intake-exhaust system,research on integrated design of aerodynamic and stealthy performance is carried out for conformal grille for the first time.And we also construct an effective numerical calculation method of aerodynamic and electromagnetic scattering characteristics for the complex grille.Firstly,based on the relevant engineering application,the design principles and guidelines are extracted,and then we construct and make the oblique import inlet of 45° coupling with straight cavity.We also make a verification on the numerical method of electromagnetic scattering characteristics by comparing experimental results with the calculation based on MLFMM.Secondly,research on the electromagnetic scattering characteristics influence of the typical geometric parameters such as the grille hole spacing,grille inclination,and grille thickness are carried out,and we also study the electromagnetic scattering characteristics with different frequencies and different polarization.And then based on the optimized conformal asymmetric S-shaped inlet,research on design and electromagnetic scattering characteristics of the conformal grille for flying wing UAV is carried out,and a scale model is made to have a stealth test to verify the numerical method of RCS calculation.Finally,the coupled numerical simulation is carried out on the internal and external flow integrated for flying wing UAV coupling conformal grille.Considering the complex change in the shape of grille entrance,the numerical simulation method is presented based on hybrid grid,and then the research on the influence of the internal and external flow is carried out with different grille hole spacing.